Coming off a disappointing quarterfinal loss at Wimbledon just more than a week ago, Venus Williams could have been promoting her new book, playing on the WTA Tour or simply resting at home after another grueling Grand Slam.

Instead, she was in downtown Washington, battling the record-setting heat Wednesday afternoon to help out at a World Team Tennis-sponsored children's tennis clinic before making her season debut for WTT's Washington Kastles against the New York Buzz.

Williams, the fourth-ranked singles player in the world, arrived at Kastles Stadium at about 4:30 p.m. with a swarm of children waiting for her. For about an hour she participated in drills and games with the children before getting in some practice. Martina Hingis, a member of the Buzz, also participated in the clinic.

"I love hitting with the kids," said Williams, who had been promoting her new book, "Come to Win," in Washington earlier in the day. "They were very good. I was so surprised. Some of the little kids could barely hold the racket; the racket was bigger than them. It's probably one of my favorite parts" of playing World Team Tennis.

"I do love the competition," Williams added. "I love being part of a team. It's very different from regular tennis."

Williams, sporting a red T-shirt and blue skirt from her clothing line EleVen, received a rousing ovation from the sellout crowd and danced her way onto the court when introduced.

After watching teammate Bobby Reynolds defeat the Buzz's Alex Domijan in men's singles, 5-3, she took the court for women's doubles. Paired with Australian Rennae Stubbs, the duo defeated Hingis and Sarah Borwell, 5-3, under the lights.

Reynolds and Leander Paes then teamed up to defeat Domijan and Scoville Jenkins, 5-2, before Williams and Hingis battled in the match's women's single set.

The former rivals met on the WTA tour 21 times in the 1990s and early 2000s, with Hingis winning 11 of the contests. Yet, the Swiss player hadn't played for three years before suiting up for the Buzz last week. A Williams victory seemed to be a virtual lock.

But on this balmy night, Williams was in for a battle. After Williams took a 2-0 lead in the set, Hingis fought back to win three games in a row.

Williams then won a hard-fought game to square things at three before Hingis took the 4-3 lead after a furious rally. Williams went on to tie the set at 4 and win it in a tiebreaker, 5-4.

"She played really well," Williams said of Hingis. "She's got so much talent and she got the experience, too. I just started going for it a little more and making a few more shots. Of course her game is consistent and to retrieve and my game is just the opposite, to go for it."

Williams then paired with Paes to oppose Hingis and Jenkins in mixed doubles, the match's final set. The Kastles duo won the set, 5-3, to complete the Kastles' 25-15 victory. Washington is now 2-1 on the season.

World Team Tennis has been an annual stop for Williams despite a full schedule that includes the WTA Tour and off-court ventures such as her clothing line. She played for the Philadelphia Freedoms last season before the Kastles, the 2009 league champions, acquired her in the offseason. This is her seventh season with WTT.

With her on board, the Kastles have the biggest names in women's tennis -- and perhaps all of tennis -- in Williams and her sister Serena.

"What I love about it is that we get to go to cities where there aren't any major [women's] tournaments, in like Philadelphia, like D.C., and we get to play for my fans there," Serena said in a conference call Wednesday afternoon. "It's so special to have the opportunity to play in front of my fans all across the United States."

Venus will play in three matches for the Kastles this season -- her final two will be in Philadelphia against the Freedoms on Thursday and on Saturday in St. Louis against the Aces. On Saturday, three-time Grand Slam winner Lindsay Davenport will be taking the court against her for the Aces.

Serena, fresh off another Wimbledon victory for her 13th career Grand Slam singles title, will make four appearances for the Kastles. Her season begins Friday in New York against the Buzz, followed by matches in Philadelphia on Tuesday, in Washington against the Kansas City Explorers on Wednesday and in New York against the Sportimes on July 15.

The sisters will not play for the Kastles in the same match because of a league rule limiting each team to one "marquee" player per match.